Air filtration systems are used in many situations to purge unwanted substances from the air. Such air filtration systems generally exist in a variety of forms, depending upon their use and function.
One type of air filtration system is the fumehood. Fumehoods provide an enclosed workspace which is isolated (or substantially isolated) from the ambient air in order to allow dangerous substances to be safely handled in the enclosed workspace without endangering nearby personnel. Fumehoods are generally either ducted or ductless. Ducted fumehoods are configured to purge hazardous substances from the air of the enclosed workspace before venting that air to the ambient atmosphere. Ductless fumehoods are configured to purge hazardous substances from the air of the enclosed workspace before venting that air to the ambient air of the room containing the ductless fumehood.
The present invention is applicable to both ducted and ductless fumehoods. In one preferred form, the present invention relates to ductless fumehoods. To this end, and for purposes of illustration but not limitation, the present invention will now be discussed in the context of ductless fumehoods.
More particularly, and looking now at FIGS. 1 and 2, there is shown a typical prior art ductless fumehood 5. Ductless fumehood 5 generally comprises an enclosed workspace 10 defined by a frame 12 and accessed by a front sash closure 15, with front sash closure 15 engaging a workbase 20 when the enclosed workspace is “sealed”. An air inlet 25 admits ambient air into enclosed workspace 10, and an air vent 30 removes air from enclosed workspace 10. Air from air vent 30 is passed through a filter 35 before being returned to the ambient air of the room (e.g., a laboratory) containing ductless fumehood 5 via an air outlet 37. Filter 35 removes hazardous substances from the air, thereby rendering the air safe before it is returned to the ambient air. An outlet fan 40 is generally provided between air vent 30 and air outlet 37 so as to keep enclosed workspace 10 at a negative pressure differential relative to the ambient air, whereby to ensure that any air within enclosed workspace 10 passes through filter 35 before being returned to the ambient air. A sensor 45 is generally provided at (or downstream of) filter 35 so as to ensure that the filter purges any hazardous substances from the workspace air before that air is returned to the ambient air. Outlet fan 40 and sensor 45 are generally connected to an alarm 50 which can alert personnel in the event that filter 35, outlet fan 40 and/or sensor 45 fail.
Ductless fumehoods have become popular due to their technical effectiveness, low acquisition and implementation costs, rapid installation and substantial energy savings. More particularly, with proper filter selection, ductless fumehoods can be extremely effective in removing hazardous substances from the air of a workspace. Furthermore, due to their simple design and their ductless nature, ductless fumehoods are relatively inexpensive to manufacture and relatively inexpensive to implement, since they do not require the extensive engineering and installation efforts normally associated with ducted fumehoods. Furthermore, installation of ductless fumehoods is fast and simple, since ductless fumehoods require little more than uncrating and initial setup and testing before use. Ductless fumehoods are also extremely energy efficient, since they return the filtered air to the ambient air of the room rather than venting the filtered air to the outside atmosphere. As a result, already-heated air is retained in the room during winter and already-cooled air is retained in the room during summer, thereby minimizing the energy required to temperature-condition the air in the room.
With ductless fumehoods, it is important to manage the airflow out of enclosed workspace 10 in order to ensure that all hazardous substances are removed from the workspace air before it is allowed to return to the ambient air of the room. Ideally, this means that all of the enclosed workspace air is passed through filter 35 before that air is allowed to return to the ambient air of the room. In practice, however, this is difficult to ensure, inasmuch as personnel must typically repeatedly and actively access enclosed workspace 10 through front sash closure 15, and hence some air from the enclosed workspace may pass into the air of the room via the open front sash closure 15 without first passing through filter 35. To limit this occurrence, and as previously discussed, outlet fan 40 is set to keep enclosed workspace 10 at a negative pressure differential relative to the ambient air, whereby to minimize unintentional airflow out open front sash closure 15. In addition, front sash closure 15 is typically arranged so as to minimize the size of the opening provided into enclosed workspace 10.
More particularly, and looking now at FIGS. 3 and 4, front sash closure 15 typically comprises a plurality of interconnected sliding panes 55. When enclosed workspace 10 is to be accessed by personnel, the bottommost pane 55 is lifted upwards, causing the interconnected sliding panes 55 to overlap in a cascading fashion whereby to progressively expose more and more of the enclosed workspace to the personnel. Thus, a conventional front sash closure 15 provides a variable-sized opening into enclosed workspace 10, with the variable-sized opening enlarging upward “from the bottom up”.
While conventional front sash closures 15 of the sort shown in FIGS. 1-4 have proven highly effective and highly reliable, they can also provide a sub-optimal solution in certain situations. More particularly, as noted above, conventional front sash closures 15 open “from the bottom up”. Thus, in situations where the objects to be manipulated (e.g., test tubes, beakers, etc.) sit directly on workbase 20 and are relatively short, the “bottom up” closure of conventional front sash closure 15 need only expose a relatively small region of enclosed workspace 10 in order to provide the personnel with appropriate access to the objects which are to be manipulated. However, in situations where the objects to be manipulated sit elevated above workbase 20 (e.g., on a stand or pole) and/or are relatively tall, the “bottom up” closure of conventional front sash closure 15 requires that a relatively large region of enclosed workspace 10 be exposed in order to provide the personnel with appropriate access to the objects which are to be manipulated. However, it will be appreciated that this is a sub-optimal solution, since it increases the possibility that hazardous substances may escape from enclosed workspace 10 through the open front sash closure 15.
It will be appreciated that the same issue can arise with respect to ducted fumehoods which use a conventional front sash closure 15 comprising the aforementioned cascading sliding panes 55.
Thus there is a need for an improved front sash closure for a ductless fumehood, and/or a ducted fumehood, which addresses the foregoing issues.